1. Field of the Invention
The subject process relates to a lithographic method for printing. More specifically, a non-film requiring process for transferring an image to a printing plate is disclosed.
2. Description of the Background Art
Traditional methods of lithographic printing for transferring an image to a printing plate have involved a step that requires the use of film. Such film requiring processes are time consuming and, including the film and associated processing machines, extremely expensive. With the advent of relatively inexpensive photocopy machines and the creation of photocopy facilities on virtually every street corner, to compete, printing houses employing standard photographic film intensive lithographic means have found a critical need for an advancement in these traditional lithographic techniques.
In an ordinary or traditional lithographic procedure for transferring an image to a printing plate the process begins by obtaining original camera ready copy by standard paste-up techniques or by computer aided typesetting or imagesetting. Screen tints and halftoned photographs are either pasted into the camera ready copy directly or specified to be placed later as part of the stripping process. If generated by desktop publishing means, all copy is digitally scanned and positioned electronically for output to film or paper.
Next, mechanical copy is shot on a graphic arts camera to produce individual film negative pages. These pages must be taken, retouched to fill in pinholes and cutlines, and then stripped into pin registered flats, usually mylar, with proper margin positioning and imposition for press and bindery specifications. Flats are then masked off to cover unwanted open areas. In stripping, press and bindery marks are incorporated into each flat or are laid up into a double exposure flat for imaging to a plate.
Using a high intensity UV light source, the flats are then proofed by contact exposure onto blueline proofing paper. Proofs are then folded and trimmed to represent the finished printer and bound product.
After approval and corrections, the film stripping flats are then used to expose the image to a photosensitive printing plate, typically negative acting. The unexposed image is dissolved away in the development process leaving an ink receptive image. After an application of preserving gum, the plates are ready for press.
In the article "Lithographic Plates by Xerography" (Penrose Annual, Vol. 45, page 134, 1951) paper lithographic plates are mentioned as being substitutional in a xerographic process for a paper sheet in the transfer operation.
More specifically, in reference to issued patents, U.S. Pat. No. 2,870,253 describes a method of production of printing surfaces. An electrical discharge is used to etch plates having a rigid electrically-conducting backing and a partially electrically-conducting surface.
A photo process is disclosed in U.S. Pat. No. 3,485,629. A positive microfilm frame is employed in this process.
A machine for copying an original, making a master from the original, and printing from the master is related in U.S. Pat. No. 3,648,603. Electrophotography is used an offset type printing machine to produce a printing master. A coating of a thin thermoplastic hydrocarbon is applied to a photoconductive surface of a sheet which makes it oleophilic. The toner image is applied in the usual manner. The oleophilic background is coated with oil and rejects an aqueous ink. The porous toner image absorbs the oil and provides a surface to which the viscous aqueous ink adheres.
U.S. Pat. No. 3,867,150 demonstrates a printing plate process and apparatus using a laser scanned silver negative. Surfaces are formed in relief such as a printing plate. The laser forms an optical mask by generating opaque areas in an essentially transparent, dry silver sheet. Heat is applied to the exposed sheet to develop the latent image. The resulting optical mask is used for imaging on a photosensitive printing plate.
U.S. Pat. No. 4,064,205 provides a method for making a printing plate from a porous substrate. A paste-up is laser scanned and the information transferred, via another laser, to a printing plate.
A processing-free planographic printing plate and method of use are described in U.S. Pat No. 4,634,659. A light source passes light through a lens having a reflective backing to strike a subject image. Light returning from the subject image reflect from the angled back surface and to a light sensitive plate.
Finally, an apparatus and printing system for developing a lithographic plate for printing are disclosed in U.S. Pat. No. 5,058,500. As usual, film is involved in the initial steps of producing a printing plate.